1. Field of the Invention
The present invention relates to a focal plane shutter for digital cameras.
2. Description of the Related Art
Two types of focal plane shutter for digital cameras are known. One includes two shutter blades: a front blade and a rear blade, and the other includes one shutter blade. The former is configured so that the front blade covers an exposure aperture in a set state, and in photography, the front blade and the rear blade are successively moved in the same direction, the front blade starts to open the exposure aperture to start exposure for photography (hereinafter referred to as photography exposure) of an image pickup device such as a CCD, and the rear blade finishes closing the exposure aperture to finish the photography exposure. Then, when imaging information is stored in a storage device from the image pickup device via an information processing circuit, a series of photography operations as a camera after release is finished.
For the latter, two photography methods are known. In either method, an exposure aperture is fully opened in a set state. In one method, an electronic control circuit controls an image pickup device to start photography exposure, and a shutter blade finishes closing the exposure aperture to finish the photography exposure. In the other method, an electronic control circuit controls an image pickup device to both start and finish photography exposure, and then a shutter blade closes an exposure aperture. In either case, after the shutter blade finishes closing the exposure aperture, imaging information is transmitted from the image pickup device via an information processing circuit to a storage device, and then a series of photography operations as a camera is finished.
The present invention belongs to a focal plane shutter for digital cameras of the former type. In the focal plane shutter of this type, a front blade and a rear blade are connected to a front blade driving member and a rear blade driving member. In photography, the driving members are rotated and moved by biasing forces of a front blade driving spring and a rear blade driving spring, and in setting, the driving members are reversely rotated to a set position against the biasing forces of the driving springs by a setting member rotated from an initial position. A configuration for maintaining the driving members in the set position until next photography conventionally includes a locking type configuration and a direct type configuration.
Specifically, the locking type configuration is such that each driving member is locked by each locking member in a set position. Thus, a setting member may be immediately returned to an initial position after each driving member is locked to each locking member by a setting operation. Alternatively, the setting member may be returned to the initial position after release of a camera and before a front blade driving member starts to be rotated by a biasing force of a front blade driving spring. In photography, when each locking member is operated by each electromagnet to unlock each driving member, a front blade and a rear blade are moved.
On the other hand, the direct type configuration is such that each driving member includes an iron scrap member, a setting member stops the iron scrap member in contact with each electromagnet by a setting operation, and maintains the state until next photography. Thus, the setting member is returned to an initial position when the iron scrap member is sucked by each electromagnet in the next photography. Then, when each electromagnet is deenergized to release each iron scrap member, each driving member is rotated and a front blade and a rear blade are moved.
Digital cameras include, as means for observing a subject image before photography, an optical finder, an electronic finder using a display device such as a liquid crystal panel, or both of the finders. Recent digital cameras need to have at least an electronic finder. In order to observe a subject image before photography using the electronic finder, an image pickup device for photography is advantageously concurrently used as an image pickup device for observing the subject image before photography. In this regard, for the focal plane shutter including only one shutter blade, an exposure aperture is always fully opened in a set state. Thus, the concurrent use of the image pickup device causes no problem in the configuration of the shutter.
However, for the focal plane shutter including two shutter blades, it is necessary that an exposure aperture is fully opened in a set state, and when a release button is pressed in photography, a front blade is first operated to cover the exposure aperture in an initial stage, and then the front blade and a rear blade are successively moved in the same direction. This provides an intricate configuration of the shutter. Japanese Patent Laid-Open No. 2001-222059 describes a focal plane shutter of a direct type. When this focal plane shutter is adopted in a camera including an optical finder and an electronic finder, a photographer can select a case of photography using an optical finder and a case of photography using an electronic finder before photography. In either case, a front blade starts to open an exposure aperture to start photography exposure, and a rear blade finishes closing the exposure aperture to finish the photography exposure.
As described above, the focal plane shutter described in Japanese Patent Laid-Open No. 2001-222059 includes two shutter blades, but can perform photography using an optical finder and also perform photography using an image pickup device for photography while observing a subject image to be photographed through an electronic finder. Specifically, for the camera described in Japanese Patent Laid-Open No. 2001-222059, when the photographer selects photography using the electronic finder, a movable mirror (quick return mirror) is maintained in an up state, and the exposure aperture is fully opened. When a release button of the camera is pressed in photography, the front blade first closes the exposure aperture, then the front blade starts to open the exposure aperture to start the photography exposure, and after a predetermined time, the rear blade finishes closing the exposure aperture to finish the photography exposure.
However, recent high-grade cameras have become increasingly multifunctional. There is such a demand that even with a focal plane shutter configured so that two shutter blades can be operated to perform photography, like a focal plane shutter including one shutter blade, a photographer can select before photography to perform photography in which an exposure aperture is fully opened in a set state, when a release button of a camera is pressed in photography, an electronic control circuit controls an image pickup device to start photography exposure with the exposure aperture being fully opened, and a shutter blade finishes closing the exposure aperture to finish the photography exposure, or photography in which an electronic control circuit controls an image pickup device to both start and finish photography exposure, and then a rear blade closes an exposure aperture.
The present invention is achieved in view of such problems, and has an object to provide a direct-type compact focal plane shutter for digital cameras that can perform photography in a mode in which a front blade closes an exposure aperture and a rear blade is retracted from the exposure aperture in a set state, and in photography, the front blade starts to open the exposure aperture to start photography exposure and the rear blade finishes closing the exposure aperture to finish the photography exposure for photography using an optical finder, and can perform photography in a mode in which both the front blade and the rear blade open the exposure aperture in the set state, and in photography, the front blade once closes the exposure aperture in an initial stage after release, and then the front blade starts to open the exposure aperture to start photography exposure and the rear blade finishes closing the exposure aperture to finish the photography exposure for photography using an electronic finder, and can also perform photography in a mode in which in photography, the front blade is not operated, but an electronic control circuit controls an image pickup device to only start the photography exposure or both start and finish the photography exposure and thus only the rear blade is operated to close the exposure aperture.